Academic Argument Against the Stoics

"It was these statements of the Stoics that Arcesilaus controverted by proving that cognition is not a criterion intermediate between knowledge and opinion" (Sextus Empiricus, Against the Logicians I.153).

"If, then, impressions are cognitive in so far as they attract us to assent and to the following of them up with corresponding action, then, since false ones also are seen to be of this kind, we must declare that the non-cognitive impressions are indistinguishable from the cognitive" (Sextus Empiricus, Against the Logicians I.405).

"They summon the Stoics to face apparent facts. For in the case of things similar in shape but differing in substance it is impossible to distinguish the cognitive impression from the false and non-cognitive. If, for example, of two eggs that are exactly alike I offer each one in turn to the Stoic for him to distinguish between them, will the Sage be able on inspection to declare indubitably whether the egg exhibited is this one or that other one? And the same argument also holds good in the case of twins" (Sextus Empiricus, Against the Logicians I.408).
Plato died in 347 BCE. The Academy itself continued under new leadership.

When Arcesilaus became its head in 267 BCE, he refocused attention within Academy on the Socratic practice of asking questions to expose the pretense to knowledge.

"Arcesilaus... was the first to suspend his judgement owing to the contradictions of opposing arguments. He was also the first to argue on both sides of a question, and the first to meddle with the system handed down by Plato" (Diogenes Laertius, Lives of the Philosophers IV.6.28).

Cicero refers to the Academy with this changed focus as "the New Academy" (Academica I.46).

Academica II.40

They bring their whole case together in a single proof as follows: some impressions are true, others false; and, a false impression cannot be perceived; but, every true impression is such that one could also have a false impression just like it. And, when two impressions are such that they don’t differ at all, it isn’t possible that one of them can be perceived, while the other isn’t. Therefore, no impression is capable of being perceived. (40)

Lucullus does not present Academic argument very clearly, but we can see the idea.

The Academics use Socrates' questioning in dialectic against the Stoics.

The Stoics think that knowledge is possible. They think that we can get and assent to cognitive impressions and withhold our assent from noncogntive impressions. The Academics try to make the Stoics contradict themselves.

1.  For every true impression, there could be a false impression "just like it."
2.  If (1) is true, then it is always necessary to withhold assent.
3.  If it is always necessary to withhold assent, then knowledge is not possible.
4.  Knowledge is not possible.

This argument is valid. The Stoics accept (2) and (3). This leaves (1).

Academica II.54

They harp on the similarities of twins or of seals stamped from signet rings. Who on our side denies that similarities exist, given that they are apparent in many things? Yet if it is enough to do away with knowledge that many things are similar to many others, why aren’t you satisfied with that, especially when we concede it? Why do you go on to maintain something the nature of things does not permit, by denying that each thing is in its own kind and just as it is, i.e., that there aren’t any shared features that don’t differ at all between two or more things? Take it as granted that eggs are very similar to eggs, and bees to bees: what are you fighting for? What are you driving at with your twins? That they are similar—the point with which you could have been satisfied—is conceded; but your idea is that they aren’t similar but absolutely identical, which simply cannot happen. (54)

The Academics talk about identical twins.

Suppose that a and b are identical twins, that a is walking toward me, and that I have the impression that a is walking towards me. The Academics argue that there is a false impression "just like" this impression. This false impression is that b is walking toward me.

It is important to distinguish the identity of indiscernibles from the indiscernibility of identicals.

The indiscernibility of indenticals is the thesis that if x = y, then x and y have all and only the same features.

This thesis is appears to be a truth about identity. The identity of indiscernibles is more controversial

You deny that there is such similarity between things in nature. ... You may well be right; but there could be one between our impressions. If so, that similarity deceives the senses—and if one similarity [involving twins] deceives them, it will render everything doubtful. For without the criterion by which he’s supposed to be recognized, even if the person you’re looking at actually is the person you think you’re looking at, you still won’t be judging by the mark you say we’re supposed to use to avoid false, but exactly alike, impressions (Academica II.84).
The Stoics accept the identity of indiscernibles. They think that if x and y have all and only the same features, then x = y. So there is some feature that distinguishes a from b.

At this point, then, the question seems to be whether the impression the person walking toward me impresses on me is clear enough for me to know the person is a rather than b.

The Stoics think that with practice I could get an impression that was clear enough.

Even I could not get such an impression, this alone would not show that (1) is true.

Academica II.57

I concede that the wise man himself—the subject of our whole discussion—will suspend his assent when confronted by similar things that he does not have marked off; and that he will never assent to any impression except one such that it could not be false. But he has a particular skill by which he can distinguish true from false impressions in normal cases and he must bring experience to bear on those similarities. Just as a mother discriminates her twins as her eyes become accustomed to them, so you, too, will discriminate them, if you practice. (57)

“Nor does this work against us, since it is all right for us not to be able to discriminate those eggs: that doesn’t make it any more reasonable to assent that this egg is that one, as if there were absolutely no difference between them. I have my rule—to judge such impressions true as cannot be false—from which I may not depart by a hair’s breadth (as they say), lest I confound everything. (58)

Lucullus makes two points.

He says that practice makes us better at distinguishing similar things.

He says that we do not need "to be able to discriminate those eggs."

How does this second point bear on the Academic argument against the Stoics?

Lucullus, it seems, is admitting that there could be false impressions "just like" some true impressions but denying that this poses a problem for the Stoics.

Academica II.61

If we followed the Academics, we would be constrained by bonds that would prevent us from moving at all. For by doing away with assent, they have done away with every mental motion and practical action—something that not only can’t be done rightly, but can’t be done at all. (61)

In response to the argument the Academics give, the Stoics give the inactivity argument.

4.  Knowledge is not possible.
5.  If (4) is true, then assent is not permitted.
6.  If assent is not permitted, rational action is not possible.
7.  Rational action is not possible.

Now the roles in the dialectic have switched.

The Stoics are inviting the Academics to admit they believe (4) but not (7).

This leaves (5) and (6).

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